(This article first appeared in SportsCar magazine’s July 2007 issue)

By Philip Royle

The best projects start with a bang. Unfortunately, this was more like a pop, followed by low-speed thunks. The thunks were accompanied by rattles, and those rattles eventually manifested themselves into a more tangible puddle of oil.

After six years and nearly 30,000 miles of abuse, the left rear shock on the 1996 Mazda Miata kicked the bucket. It did so on the way back from an autocross – at least it went out in the line of duty.

The car had originally been purchased for daily transportation, but not being able to leave well enough alone, the car soon found a number of goodies bolted to it. In the moment before the shock opted show the world its smelly, oily goodness, the car was sitting atop a set of 16-inch aftermarket wheels with horridly old tires, had a Hard Dog roll cage, some Racing Beat sway bars and adjustable end links, Mazdaspeed braided steel brake lines and, of course, four good Tokico Illumina shocks with Vogtland springs. Then came the bang.

The Tokicos can’t be blamed for giving out. The suspension had seen many lapping days at various Southern California tracks, and had also competed in an uncountable number of autocrosses. The shocks were designed for the street, not the track, and a blown shock is sometimes the price you pay for not following directions.

The bang also happened at an interesting point in the car’s life. While once serving as daily transport to and from the office, the Miata now only sees the street when it’s on its way to some kind of competition, usually autocross. Now that the shocks needed replacing, it was time to rethink the entire setup.

A plan is formed

As it was, the Miata was an STS2 Solo car, but not a very competitive one. The limiting factors in the car’s regional competitiveness were shocks, springs and, of course, the decrepit tires.

After perusing the options, it was decided that constructing a nationally competitive STS2 car wasn’t in the cards. Rather, the goal would be to build a car that could both autocross and Club race on a regular bases, with the knowledge that the Miata would probably wind up not dominating either. That’s right, this car is going to be a compromise – but a fun compromise.

To determine the best method to go about this, we headed to the rulebooks. Since the Miata was a first generation 1.8L car lacking the differential, it only made sense to build it to Solo’s STS2 class. Once the car was up to speed in Street Touring, a cage would be welded in, a race seat would be mounted and the car could compete in Club Racing’s Improved Touring A. At that point, the car’s Solo classification would shift from STS2 to C Street Prepared, and further modifications could be made – like adding the needed diff.

The goal for now, however, is to build a car with parts that cross from Solo to road racing, making the leap to Club Racing far more affordable.

Sounds like a plan.

Parts are ordered

The first step was deciding which shocks and springs to use. Since the car rarely sees daily commuting, this was simple: we needed race coilovers.

About two years ago, Koni released its 8041 RACE series of adjustable dampers. Koni’s goal was to design a race shock that would hold up to both Solo or Club Racing duties. An added bonus was that a set of four shocks could be purchased for under $1,000 – not too shabby. Last year, the company expanded its lineup, and with it, an application for the Miata. Pay dirt.

With the shocks ordered, we started our search for quality race springs. Koni’s 8041 RACE dampers were valved for a variety of spring rates, so we decided a safe starting place for spring rates would be to follow the Spec Miata lead and order 700lbs. front springs and 325lbs. rears. The Koni’s can fit both 2.25-inch inner diameter (ID) springs and (with an adapter) 2.5-inch springs. After some searching, we finally ordered a set of Eibach’s 2.25-inch ID 6-inch tall front and 7-inch tall rear ERS race springs. We also ordered a couple helper springs and spacers.

This setup should also complement the Racing Beat front and rear sway bars and adjustable end links that are already on the car.

If the Miata were to eventually wear ITA stickers, the current 16-inch aftermarket wheels would have to go. STS2 rules allow for any wheels 7.5-inches wide or narrower and CSP’s wheel rules are also relatively open. However, Club Racing’s General Competition Rules state ITA cars that came stock with 14-inch diameter wheels (as the Miata did) can step up to a maximum of 15-inch diameter wheels with a maximum width of 7 inches. Consequently, the search was on for a set of affordable and lightweight 15x7s that would look nice on the car.

Motegi Racing offers a variety of performance wheels, and it’s also one of only a handful of companies that offer a lightweight 15×7 wheel in flat black – since the car’s hardtop is flat black, this was viewed as a sign, and Motegi Traklite 1.0 wheels were ordered. When the wheels arrived, they were tossed on the scale to see if these lightweight wheels stood up to the claim. The scale measured the wheels at 10lbs. 15oz. each. They weren’t kidding – these are light. Plus they look darned good on the car and were relatively affordable at $232 a piece.

Tires was an interesting subject. Anyone looking to compete with Improved Touring cars would need DOT-legal R compound tires; however, STS2 rules mandate a UTSG rating of 140 or greater and a tread width of 225mm or smaller. A popular tire in the class is the Falken Azenis, but by all measures, the Hankook Ventus R-S2 should be competitive in the class. Consequently, we ordered a set of the 205/50-15 Hankooks. Our experience in the past on Hankooks has proven positive, and we wanted to see how these would fare against the competition.

The final part ordered was a lightweight battery. STS2 and CSP rules are very forgiving when it comes to battery replacement, allowing for virtually any battery with a similar OE voltage to be bolted into the car in a variety of locations. ITA rules, however, are more specific, stating that batteries must be of “similar” weight and are fitted in the standard location.

Because we prefer non lead-acid batteries, and we’re suckers for carbon fiber, we ordered the B106 race battery from Braille Auto Development. The Braille battery measures 5.75 inches across, 4.25 inches tall and 3.25 inches deep (the stock battery is 7.5 inches across, 7.25 inches tall, 5 inches deep). We also ordered Braille’s billet battery tie down. The Braille battery tipped our scales at 7lbs. 7oz., and the bracket weighed about a pound. We also ordered Braille’s battery charger wince we’ve been known to drain a battery or two.

We’re pretty sure this battery won’t fly in ITA (despite installing it close to the factory location). Should it prove really, really illegal in Club Racing, we’ll move the battery to one of our other project cars because, well, carbon fiber batteries are too cool to pass up.

We also thought it time to order a complete set of magnetic numbers, so we did so by calling Solo Performance Specialties (SPS). The company has long supported autocross, and its owners are active SCCA members. Also, we were tired of taping numbers to the side of the car every time we competed. SPS also sent out a set of STS2 letters – if we’re not going to win, at least we’re going to look like we know what we’re doing.

Installations are completed

Step one was to ditch the blown shock. For that, we headed to Shoreline Motoring in Huntington Beach, Calif. We’ve used Shoreline in the past, and we’ve grown to love the shop. While the shop’s clientele aren’t necessarily having the shop wrench on their race cars, Shoreline’s one of a few shops that offers good, honest advice, doesn’t charge extortionate fees and uses torque wrenches on parts that require them.

During the installation, the decision was made to run the helper springs in the front only, and to move the threaded collar mounts down one notch on the shock bodies. Shoreline also modified the factory bump stop, retaining the rubber spring seat and replacing the stock bump stop with the supplied Koni unit (this required drilling out the factory spring seat to fit over the Koni shaft).

While at Shoreline, we also had the car aligned. For an alignment starting point, we decided to look at what two forces in the Miata world were doing. With a little online searching, we found Jim Daniels’ Spec Miata setup as well as Andy Hollis’ STS2 Miata setup. We opted to start with the Jim Daniels Spec Miata alignment, with the knowledge that we’d have to dial the toe by hand as needed for autocross. As it stands, our alignment is:

FRONT
Camber: -2 degrees
Caster: +3.5 degrees
Toe: 0

REAR
Camber: -2 degrees
Toe: 0 degrees

The car’s ride height is set at 5.25-inches from the ground to the bottom of the pinch weld.

The car’s previous settings were -1.2 degrees negative front camber, -1 degree rear camber, and a hint of toe out in the front. The finished result is a car that definitely turns in slower than before – it’s obvious we’re going to have to tweak the toe settings for Solo.

Also, the car has yet to be corner balanced. This is something we’ll tackle in a later installment.

The battery installation was simple. Parts of the factory battery hold down were removed and the billet aluminum Braille brace was bolted in. To mount the Braille unit, we marked the holes we’d need, pre-drilled four holes, and then attached the base using the supplied screws – which, incidentally, hold the battery far more securely than the factory setup.

The car is far from done, and in fact, we have yet to take the car to an autocross with its current setup. Street driving, however, has shown that the linear Eibach springs are far firmer on small bumps than the previous progressive springs. While that leads to a more abusive ride, it also results in a more predictable feel, especially from the back of the car, over transitions – and with the Koni’s adjustment set halfway between soft and hard, the ride, while stiff, isn’t completely out of the realm of being drivable on a daily basis. The full hard shock setting, however, should only be used for competition.

As for the Hankook tires, our experience in other cars with the Ventus R-S2 tires, have shown the tires to display a predictable breakaway while offering ample grip for a street tire. And while we didn’t, we would recommend shaving the tires if competition is your primary goal. Shaving would reduce the tread squirm that most full tread depth tires suffer from. To better evaluate these tires, we have a couple tests in the works.

The clock is ticking on this project. Our goal is to have the Miata’s logbook by early next year, but to do so, we’ve got to raid a couple parts bins, take care of a couple maintenance issues, fix a slipping clutch and finally weld in a roll cage – all without going broke, and – even more importantly – not compromising the car’s performance to the extent that we wind up with a car that isn’t good at anything.

SOURCES:
Braille Auto Development, (941) 312-5047, http://www.brailleauto.com
Eibach Springs, (800) 507-2338, http://www.eibach.com
Hankook, http://www.hankooktireusa.com
Koni http://www.koni.com
Motegi Racing, (866) 4MOTEGI, http://www.motegiracing.com
SPS Performance, (877) 614-SOLO, http://www.soloperformance.com

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